docs: def decode(cls, line):
          """
          Remove backslash escaping from line.valueDecode line, either to remove
          backslash espacing, or to decode base64 encoding. The content line should
          contain a ENCODING=b for base64 encoding, but Apple Addressbook seems to
          export a singleton parameter of 'BASE64', which does not match the 3.0
          vCard spec. If we encouter that, then we transform the parameter to
          ENCODING=b
          """
          if line.encoded:
              if 'BASE64' in line.singletonparams:
                  line.singletonparams.remove('BASE64')
                  line.encoding_param = cls.base64string
              encoding = getattr(line, 'encoding_param', None)
              if encoding:
                  line.value = codecs.decode(line.value.encode("utf-8"), "base64")
              else:
                  line.value = stringToTextValues(line.value)[0]
              line.encoded=False